Utilizing Protein During Weight Loss to Impact Physical Function and Bone

The ancillary study to the UPLIFT trial (NCT03074643) will use a 3-group design in 225 obese (body mass index \[BMI\] 30-45 kg/m2 or 27-\<30 kg/m2 with an obesity-related risk factor), older (65-85 years) men and women at risk for disability (Short Physical Performance Battery, SPPB ≤10) who will undergo a 6-month weight loss intervention followed by a 12-month follow-up phase to test the overall hypothesis that a higher protein (1.2 g/kg body weight/day) / lower carbohydrate (CHO) diet during a 6-month weight loss intervention improves bone phenotypes compared with an isocaloric lower protein (the current Recommended Dietary Allowance (RDA), 0.8 g/kg body wt/d) / higher CHO diet, and whether continuing a higher protein / lower CHO diet for 12-months following weight loss will result in better maintenance of bone. All participants will undergo a 6-month weight loss intervention involving caloric restriction and supervised exercise followed by 12 months of follow-up with randomization to one of three groups (n=75/group): 1) Lower protein / higher CHO diet for the 6-month weight loss phase only (RecProt); 2) Higher protein / lower CHO diet for the 6-month weight loss phase only (6-mo HiProt); or 3) Higher protein / lower CHO diet for the 6-month weight loss and 12-month follow-up phases (18-mo HiProt). Vertebral and femoral volumetric bone mineral density and cortical thickness (Primary Aim) and bone marrow adipose tissue (Secondary Aim 1) will be assessed with computed tomography at baseline, 6-, and 18-months. Bone strength and fracture risk (Secondary Aim 2) will be assessed by finite element modeling at baseline, 6-, and 18-months.